The present invention relates to a tool for chip removing machining comprising a relatively tough core connected to a relatively wear resistant outer periphery, and to methods and apparatus for making the tool.
It is previously known through for example WO 98/28455 to press a core and a surrounding tube of material powder in two steps. The material powder comprises wolfram carbide (WC), also known as tungsten carbide, together a with cobalt (Co) binder that are compressed between a punch and a die, and that subsequently are sintered such that the binder metal is melted and binds the carbide to form a tool material for chip removing machining. Thus, there results a tube formed around, and connected to, an inner core. The core has a higher binder (cobalt) ratio than does the tube, whereby the core is tougher than the tube, but the tube is harder and more wear resistant than the core.
That known technique brings about a plurality of drawbacks during manufacture of elongated slender bodies. The powder gives off dust, and the formed green body (pressed but not sintered material) will not endure handling to any degree. Furthermore the chip flutes must be formed by grinding which is time consuming. The problems have partly been solved by the injection molding of hard metal mixed in a carrier such as indicated in U.S. Pat. No. 5,947,660. The method of injection molding brings about a high degree of freedom concerning geometry but brings about troubles during manufacture of elongated slender bodies and costly investments in molds.
U.S. Pat. No. 4,779,440 discloses that an extruded drill blank having chip flutes of constant pitch along the circumference of the blank can be obtained by heating a hard metal powder to extrusion temperature, and pressing the heated powder under high energy consumption through a space defined by a mandrel and a nozzle while rotating the blank. The blank is guided during the extrusion step past a helical ridge provided inside of the nozzle, to shape chip flutes along the blank. A drawback of the known technique is that the useful life of the tool is less than desired.
One object of the present invention is to provide a method and a device, whereby the drawbacks of the known technique are eliminated.
Another object of the present invention is to provide a method and a device whereby elongated slender bodies can be manufactured having optimum length of service time.
These and other objects have been achieved by a method and a device for manufacturing a tool, as well as a tool itself. The method aspect of the present invention involves a method for manufacturing a tool for chip removing machining. The tool comprises a central portion disposed within an outer peripheral portion. The central portion is formed of a tougher, less wear-resistant material than the outer peripheral portion. The method comprises the steps of:
A) feeding a warm first plastic compound comprised of a hard material and metallic binder to an inner extrusion die for forming the central portion;
B) simultaneously feeding a warm second plastic compound comprised of a hard material and metallic binder to an outer extrusion die arranged coaxially with the first die, for forming the outer peripheral portion coaxially around the first plastic compound, whereby the second plastic compound abuts the first plastic compound during the extrusion, the second plastic compound being more rear-resistant and less tough than the first plastic compound; and
C) heating the first and second plastic compounds as a unit to drive off a polymer present in those compounds and to sinter the remainder of those compounds into a hard blank.
Another aspect of the invention pertains to an apparatus for making a tool for chip forming machining. The apparatus comprises a housing having a recess extending therethrough for conducting extruded material. First and second coaxial nozzles are arranged for coaxially conducting first and second compounds into an inlet end of the recess, for forming a central core and an outer tube connected to the central core. A die disposed in the recess contains a hole through which the first and second compounds pass.
The invention also pertains to a tool for chip removing machining which comprises a center core and an outer tube. The center core and the outer tube are formed of respective first and second compounds, wherein the first compound is tougher and less wear-resistant than the second compound. The tool includes a front cutting edge and a chip flute for each cutting edge. The chip flute is disposed entirely in the outer tube. The tool is formed by the steps of:
A) feeding the first and second compounds to first and second coaxially arranged dies, whereby the first and second compounds form the core and the tube, respectively; and
B) heating the first and second compounds as a unit to drive off a polymer contained by the first and second compounds, and to sinter the remainder into a hard blank.